Liquid Crystalline State Research Articles

Nanoscale Imaging of the Piezoelectric Effect of Bilayer Phospholipid Molecules of Cell Membrane using Piezoresponse Force Microscopy∗

The dynamic piezoelectric effect of the plasma membrane and the nuclear envelope of rat A7r5 aorta smooth muscle cell is imaged with sub-3 nm spatial resolution using Piezoresponse Force Microscopy (PFM). The results verify that cell membrane is piezoelectrically active due to ordered arrangement of polar phospholipid molecules in the liquid crystalline state. A detailed analysis of the PFM signals with a 10 V / 0 V / −10 V DC bias voltage and a 10 V AC voltage at a frequency of 2 kHz reveals piezoelectricity of cell membrane perpendicular to membrane surface Consequently, our results indicate that compression or tension of the membrane structure will lead to the change of membrane potential, suggesting the piezoelectricity of cell membrane plays an important role in physiological activities of cells such as cells communication and material transport. ∗This work is supported by the National Natural Science Foundation of China (No. 10804085 and 10774113).

Poly(Ethylene Glycol) in Drug Delivery, Why Does it Work, and Can We do Better? All Atom Molecular Dynamics Simulation Provides Some Answers

Abstract We summarize our recent work, using all atom molecular dynamics simulation to study the role of poly(ethylene glycol) (PEG) in drug delivery. We have simulated the drug delivery liposome membrane, in both the Gel and Liquid crystalline states. The simulations of the PEGylated membrane have been carried out in the presence of a physiological concentration of NaCl, and two other salts encountered in physiological conditions, KCL and CaCl 2 . We also simulated targeting moieties on the PEGylated membrane, comparing the behavior of two targeting moieties. We also simulated PEG with three drug molecules for which it is used as a delivery aid: paclitaxel, piroxicam, and hematoporphyrin. We found that the specific properties of PEG, its solubility in both polar and non-polar solvents, and its acting as a polymer electrolyte, have a significant e_ect on its behavior when used in drug delivery.

Thermal adaptation of the archaeal and bacterial lipid membranes.

The physiological characteristics that distinguish archaeal and bacterial lipids, as well as those that define thermophilic lipids, are discussed from three points of view that (1) the role of the chemical stability of lipids in the heat tolerance of thermophilic organisms: (2) the relevance of the increase in the proportion of certain lipids as the growth temperature increases: (3) the lipid bilayer membrane properties that enable membranes to function at high temperatures. It is concluded that no single, chemically stable lipid by itself was responsible for the adaptation of surviving at high temperatures. Lipid membranes that function effectively require the two properties of a high permeability barrier and a liquid crystalline state. Archaeal membranes realize these two properties throughout the whole biological temperature range by means of their isoprenoid chains. Bacterial membranes meet these requirements only at or just above the phase-transition temperature, and therefore their fatty acid composition must be elaborately regulated. A recent hypothesis sketched a scenario of the evolution of lipids in which the “lipid divide” emerged concomitantly with the differentiation of archaea and bacteria. The two modes of thermal adaptation were established concurrently with the “lipid divide.”

Membrane Area Deformation under Osmotic Stress: Deuterium NMR Approach

We address the hypothesis that the sensitivity of lipid bilayers to pressure, temperature, and osmotic stress represents influences of non-specific lipid-protein interactions on functions of cellular membranes [1,2]. Measurements of membrane structural parameters such as bilayer thickness and area per lipid employ a mean-torque analysis [3] of 2H solid-state NMR order parameters (SCD). NMR lipid order parameters are very sensitive to changes in cross-sectional area per molecule. We observed striking (≈20%) changes in structural properties (decrease in area per lipid and increase in bilayer thickness) when ≈200 atmospheres of pressure (dehydration pressure or osmotic pressure) are applied to lipid (DMPC) bilayers in the liquid-crystalline state. We show the equivalence of osmotic and dehydration pressures by NMR experimental measurements as well as thermodynamically [2]. The elastic area compressibility modulus (Ka) of bilayers is determined by employing different pressure techniques in combination with NMR and vapor pressure osmometry methods. Our findings agree well with the reported Ka value for DMPC [4] obtained with a much smaller range of osmotic pressures. However, we observe an additional variation in Ka determined at higher osmotic pressures, where the role of complex dynamics in the bilayer structural changes becomes more evident. We propose that the hierarchy of forces and motions is perturbed by membrane dehydration (osmotic pressure) due to the alteration of interlamellar spacings, with corresponding changes in elastic area compressibility moduli. Our findings have significant implications for the applicability of solid-state 2H NMR spectroscopy together with membrane stress techniques for understanding the mechanisms of action of pressure-sensitive proteins.[1] A.V. Botelho et al. (2006) BJ 91, 4464-4477.[2] K.J. Mallikarjunaiah et al. (2011) BJ 100, 98-107.[3] H.I. Petrache et al. (2000) BJ 79, 3172-3192.[4] H.I. Petrache et al. (1998) CPL 95, 83-94.

Quinolinium and isoquinolinium ionic liquid crystals

Ionic liquid crystals based on quinolinium and isoquinolinium salts were prepared by quaternization of quinoline and isoquinoline, respectively. In the first place the influence of the alkyl chain on the thermal behaviour was investigated. Two types of (iso)quinolinium salts were synthesized. Long-chained (iso)quinolinium cations (with chain lengths varying from C12H25 to C22H45), with the inclusion of the odd homologues C17H35 and C19H39, were combined with the spherical anions bromide, tetrafluoroborate (BF4−) and hexafluorophosphate (PF6−). Dodecyl sulfate, dioctyl-, dihexyl- and dicyclohexylsulfosuccinate anions allowed the introduction of anions with (long) alkyl chains. It is shown that a subtle balance between strong electrostatic forces and the degree of disorder originating from molten alkyl chains is crucial for mesophase formation. The influence of the anion size on the mesophase behaviour was studied. Smectic A phases were observed for the long chain analogues of the bromide, tetrafluoroborate and hexafluorophosphate salts. The minimum alkyl chain length needed to induce mesomorphism increases when the bromide is exchanged by more voluminous anions, while the transition temperatures are lowered. The introduction of an alkyl chain in the anionic part drastically changes the thermal behaviour. The dodecyl sulfate salts show smectic A phases for cations with much shorter chain lengths than the other anions. For the dioctylsulfosuccinate salts this trend is even more pronounced, as the N-methyl(iso)quinolinium dioctylsulfosuccinate salts exhibited enantiotropic smectic A phases at ambient temperature. Structural models for the packing of the quinolinium and isoquinolinium salts in the liquid-crystalline state are presented, as well as the crystal structures of N-octylquinolinium dodecyl sulfate and N-octylisoquinolinium bromide.

Mesogen induced self-assembly for hybrid bulk heterojunction solar cells based on a liquid crystal D–A copolymer and ZnO nanocrystals

A new donor–acceptor type liquid-crystalline copolymer, poly[3-(6-(cyanobiphenyoxy)thiophene)-alt-4,7-(benzothiadiazole)], P3HbpT-BTD, was designed via copolymerization of liquid-crystalline electron-donating thiophene units and electron-accepting benzothiadiazole (BTD) units. The nanostructure and photoelectric properties of the copolymer under different thermal treatment conditions were systematically investigated. Studies of the relationship between the annealing conditions and the nanostructures of the copolymer revealed that the cyano-biphenyl mesogenic units could induce the copolymer chains into a well ordered lamella structure upon annealing at the liquid crystalline state temperature. When the hybrid films of P3HbpT-BTD/ZnO nanoparticles (NPs) were annealed at a temperature below or above the mesophase temperature region, less ordered copolymer chains resulted in an undeveloped interpenetrating network and caused great aggregation of ZnO NPs. Most strikingly, the hybrid film annealed at the liquid-crystalline state temperature (180 °C) achieved a well-dispersed and highly oriented nanoscale assembled nanoparticle region. The spontaneous self-organization of P3HbpT-BTD enhanced the crystallinity and orientation of the ZnO NPs. Therefore, the resulting nanoscale phase separation of the hybrid films led to well-ordered percolated networks. Hybrid bulk heterojunction photovoltaic devices based on the copolymer P3HbpT-BTD and ZnO NPs were fabricated under different annealing treatments. A maximum power conversion efficiency of 1.98% was achieved upon annealing at the mesophase temperature (180 °C).

Comb-shaped liquid crystalline stereoregular cyclolinear methylsiloxane copolymers: synthesis, behaviour in bulk and behaviour in monolayers

Stereoregular cyclolinear organosiloxane copolymers containing vinyl groups with diorganosiloxane spacers as well as cyclohexasiloxane fragments were synthesised. Comb-shaped liquid crystalline (LC) cyclolinear polymethylsiloxanes with mesogenic side groups were prepared by hydrosilylation of stereoregular cyclolinear organosiloxane copolymers with (4′-cyanobiphenyl-4-yl)-11-(1,1,3,3-tetramethyldisiloxyl)undecanoate in the presence of the Karstedt catalyst. The chemical structure of the copolymers synthesised was confirmed by proton and silicon nuclear magnetic resonance spectroscopies and infrared spectroscopy. Their phase behaviour was characterised by differential scanning calorimetry, X-ray analysis and optical polarising microscopy. It was shown that the appearance of the LC state, the temperature range of its existence and polymesomorphism are determined by the molecular mass of the copolymer and by the content of the mesogenic groups. The introduction of three mesogenic groups per monomer unit results in polymesomorphic transitions. The tacticity of the backbone influences the interchain distances in the comb-shaped LC cyclolinear methylsiloxane copolymers. Studying the Langmuir films of the stereoregular LC methylsiloxane copolymers revealed that different types of molecular arrangements could be observed depending on the number of mesogenic groups attached. LC copolymers having three mesogens per monomer unit demonstrate a two-stage monolayer collapse.

Modeling the influence of adsorbed DNA on the lateral pressure and tilt transition of a zwitterionic lipid monolayer

Certain lipid monolayers at the air-water interface undergo a second-order transition from a tilted to an untilted liquid-crystalline state of their lipid hydrocarbon chains at sufficiently large lateral pressure. Recent experimental observations demonstrate that in the presence of divalent cations DNA adsorbs onto a zwitterionic lipid monolayer and decreases the tilt transition pressure. Lowering of the tilt transition pressure indicates that the DNA condenses the lipid monolayer laterally. To rationalize this finding we analyze a theoretical model that combines a phenomenological Landau approach with an extension of the Poisson-Boltzmann model to zwitterionic lipids. Based on numerical calculations of the mean-field electrostatic free energy of a zwitterionic lipid monolayer-DNA complex in the presence of divalent cations, we analyze the thermodynamic equilibrium of DNA adsorption. We find that adsorbed DNA induces a 10% reduction of the electrostatic contribution to the lateral pressure exerted by the monolayer. This result implies a small but notable decrease in the tilt transition pressure. Additional mechanisms due to ion-ion correlations and headgroup reorientations are likely to further enhance this decrease.

Triangular arylene ethynylene macrocycles: syntheses, optical, and thermotropic liquid crystalline properties

A series of triangular, shape-persistent arylene–ethynylene macrocycles (AEMs) of related structures were synthesized and studied, with a focus on their mesomorphic behavior in correlation with their chemical structure. Generally, these discotic molecules decorated with flexible side chains demonstrated a propensity to form thermotropic liquid-crystalline (LC) phases. Characterized by differential scanning calorimetry (DSC), polarized optical microscopy (POM), and X-ray diffraction (XRD), four of the eight investigated macrocycles manifested thermodynamically stable mesophases, featuring discotic nematic or columnar structures. Longer alkyl side chains were found more conducive to mesophases, and the alkoxycarbonyl functionality was a more effective side-chain linkage at inducing and stabilizing the LC states than the alkoxy side group. The size and structure of the cyclic aromatic backbone influenced both the occurrence and type of mesophase exhibited.

Influence of temperature on dynamics of birefringence switching in photochromic nematic phase

We present results of dynamic and fast switching of birefringence in a photochromic liquid-crystalline system as a function of the sample temperature. The system consists of photochromic molecules of 4-heptyl-4′-methoxyazobenzene showing a liquid-crystalline nematic state close to room temperature. An experiment of dynamic birefringence switching was done in optical Kerr-effect set-up, where for the sample excitation, a picosecond-pulsed laser was used. Measurements were done for different temperatures of the sample in the liquid-crystalline nematic phase. We have proposed a mathematical model of dynamic, fast, and fully reversible birefringence changes. Theoretical estimations and experimental results have shown very good agreement.

Molecular-dynamic simulation of DPPC bilayer in different phase state: Hydration and electric field distribution in the presence of Be2+ cations

New molecular-dynamic topology of phosphatidylcholine bilayer (DPPC) in total atomic OPLS force field was developed and used to study the structural characteristics of liquid-crystalline and gel state of lipid bilayer in the absence and in the presence of Na+ and Be2+ cations adsorbed at the interface and different in their affinity. The parameters of bilayer geometry, the amount of surface water, and the electrostatic potential distribution were estimated quantitatively from the simulation in both phase states. The azimuthal angle of hydrocarbon chains was found nearly the same in the region of each monolayer in gel state. The amount of surface water decreases upon bilayer “freezing” mainly by loss of water molecules not participating in H-bonds between lipid headgroups. The cation adsorption was shown to have a small effect on these H-bonded water molecules, whereas Be2+ appeared to retain surface water in the bilayer upon its freezing. The electric potential distribution in the normal direction to the membrane-water interface had a similar shape in any bilayer phase state regardless of the presence of the adsorbed cations. Analysis of the microscopic nature of the electric potential revealed a mutual compensation of the contributions of the main structural components of the system (lipids, water, and ions). The boundary potential increased by 116 mV for pure DPPC, by 212 mV in the presence of Na+, and by 133 mV in the presence of Be2+ upon the phase transition of bilayer to the gel state. The boundary potential difference in the presence of Na+ and Be2+ and its change at the bilayer phase transition are in a good agreement with the experimental data published earlier [Ermakov Yu.A., 1993].

Fluorescence properties of a composite material based on the 5CB nematic liquid crystal with gold nanoparticles

The steady-state and time-resolved fluorescence spectra of n-pentyl-n′-cyanobiphenyl and a related composite material with gold nanoparticles in the liquid crystalline and solid states have been investigated. The introduction of gold nanoparticles into the liquid crystal leads to a noticeable quenching of fluorescence in the emission region of the predimer and excimer states of cyanobiphenyl. In the solid phase, a quenching of free excitons and a short-wavelength shift of fluorescence bands have been observed.

Ordered microstructure induced by orientation behavior of liquid-crystal polythiophene for performance improvement of hybrid solar cells

Control of the nanoscale morphology or microstructure of the active layer in hybrid solar cells is critical to ensure the high device performance. Here, a novel electron-donor material, liquid-crystalline polythiophene containing a cyano-biphenyl mesogenic pendant, poly[3-(6-(4-cynaobiphenyloxy)-hexyl) thiophene] ( P3HbpT), was rationally designed and synthesized. The spontaneous orientation of cyano-biphenyl mesogen endowed the P3HbpT with a well ordered morphology and facilitated the homogeneous dispersion of ZnO nanoparticles in the composites. The P3HbpT/ZnO composite films exhibited a red-shift absorption (12 nm), the lower LUMO and more ordered domains after undergoing annealing at liquid crystal (LC) states temperature (175 °C), which indicated that the spontaneous assembly behavior of the liquid-crystalline polythiophene could induce the ZnO nanoparticles to form nano-dispersing structure with highly oriented channel layers upon heating at liquid crystalline states. Furthermore, the hybrid bulk-heterojunction devices based on P3HbpT/ZnO active layer have been constructed. Without extensive optimization, the devices undergoing annealing at LC state yielded a V oc of 0.83 V and power conversion efficiency (PCE) of 0.61%, showing a significantly increased J sc and FF with respect to the un-annealed counterpart.

A Calorimetric and Spectroscopic Comparison of the Effects of Lathosterol and Cholesterol on the Thermotropic Phase Behavior and Organization of Dipalmitoylphosphatidylcholine Bilayer Membranes

We performed differential scanning calorimetry (DSC) and Fourier transform infrared (FTIR) spectroscopic measurements to study the effects of lathosterol (Lath) on the thermotropic phase behavior and organization of dipalmitoylphosphatidylcholine (DPPC) bilayer membranes and compared our results with those previously reported for cholesterol (Chol)/DPPC binary mixtures. Lath is the penultimate intermediate in the biosynthesis of Chol in the Kandutsch-Russell pathway and differs from Chol only in the double bond position in ring B, which is between C7 and C8 in Lath and between C5 and C6 in Chol. Our DSC studies indicate that the incorporation of Lath is more effective than Chol in reducing the temperature and enthalpy of the DPPC pretransition. At lower sterol concentrations (≤10 mol %), incorporation of both Lath and Chol decreases the temperature, enthalpy, and cooperativity of the sharp component of the main phase transition of DPPC to a similar extent, but at higher sterol concentrations, Lath is more effective at decreasing the phase transition temperature, enthalpy, and cooperativity than Chol. These results indicate that at higher concentrations, Lath is more disruptive of DPPC gel-state bilayer packing than Chol is. Moreover, incorporation of Lath decreases the temperature of the broad component of the main phase transition of DPPC, whereas Chol increases it; this difference in the direction and magnitude of the temperature shift is accentuated at higher sterol concentrations. Although at sterol concentrations of ≤20 mol % Lath and Chol are almost equally effective at reducing the enthalpy and cooperativity of the broad component of the main phase transition, at higher sterol levels Lath is less effective than Chol in these regards and does not completely abolish the cooperative hydrocarbon chain melting phase transition at 50 mol %, as does Chol. These latter results indicate that Lath both is more disruptive with respect to the low-temperature state of the sterol-enriched domains of DPPC bilayers and has a lower lateral miscibility in DPPC bilayers than Chol. Our FTIR spectroscopic studies suggest that Lath incorporation produces a less tightly packed bilayer than does Chol at both low (gel state) and high (liquid-crystalline state) temperatures, which is characterized by increased H-bonding between water and the carbonyl groups of the fatty acyl chains in the DPPC bilayer. Overall, our studies indicate that Lath and Chol incorporation can have rather different effects on the thermotropic phase behavior and organization of DPPC bilayers and thus that the position of the double bond in ring B of a sterol molecule can have an appreciable effect on the physical properties of sterol molecules.

Ionically Self-Assembled Thermotropic Liquid Crystalline Complexes of Linear Polysiloxane and Dendritic Amphiphiles

A series of polyelectrolyte-dendritic amphiphilic complexes with high degrees of substitution were prepared by ionic self-assembly of the polyelectrolyte poly (3-aminopropyl) methylsilane hydrochloride (PSI) with dendritic 3,4,5-tris(n-alkan-1-yloxy)-benzoic acid potassium salt [(3,4,5)nG1-COOK, n = 8, 10, 12, 14, and 16, where n was the number of carbon atoms in the alkyl tail]. These complexes PSI-(3,4,5)nG1 were characterized with wide-angle X-ray diffraction (WAXD), small-angle X-ray scattering (SAXS), Fourier transform infrared (FT-IR), thermogravimetry (TG), differential scanning calorimetry (DSC), and polarized optical microscopy (POM). WAXD profiles indicated a transition from liquid crystalline (n = 8, 10) to crystalline phase (n = 12, 14, and 16) in the PSI-(3,4,5)nG1 resulted from the dendritic amphiphiles at room temperature. PSI-(3,4,5)nG1 (n = 8, 10) were found to be in the hexagonal columnar (Φh) liquid crystalline phase, with the lattice parameter a = 3.05, 3.35 nm for n = 8, 10, respectively. On the other hand, PSI-(3,4,5)nG1 (n = 12, 14, and 16) formed end-to-end bilayer lamellar crystalline structures with the long periods d = 4.56, 5.04, and 5.68 nm for n = 12, 14, 16, respectively, at room temperature. An ionic thermotropic liquid crystalline state was obtained from PSI-(3,4,5)nG1 at temperatures: (a) below the clearing point Ti (n = 8, 10), and (b) between the melting point Tm and Ti (n = 12, 14, and 16). This research provides an easy way to obtain complexes with high degrees of substitution through the self-assembly of the linear polysiloxane and dendron amphiphiles, and demonstrates that the alkyl tail lengths of the bound dendritic amphiphiles play an important role in determining the mesomorphous structure for the polyelectrolyte-dendritic amphiphile complexes.

Self-assembled mesogens modified fullerene for efficiently stable bulk heterojunction solar cells

A facile approach to develop a novel soluble liquid-crystalline fullerene derivative, N-methyl-2- [(4-(4′-cyano)biphenyloxy)hexyloxyphenyl)]-3,4-fulleropyrrolidine, C 60 -bp-CN is reported. Compared to C 60 , the modified C 60 -bp-CN shows broadened light harvesting and lower LUMO level (−4.2 eV), ascribing to the strong intermolecular interaction induced by self-assembled cyanobiphenyl mesogens, especially after thermal annealing from liquid crystalline states. When blended with poly(3-hexylthiophene) ( P3HT), the absorption of the blend film is red-shifted to 700 nm, and the intensity is also remarkably increased. The results indicate that the modified C 60 -bp-CN is a promising acceptor for polymer solar cells (PSCs) based on BHJ active layers. Therefore, solar cell devices based on an ITO/PEDOT:PSS/ P3HT:C 60 -bp-CN/LiF/Al configuration are fabricated. Clearly, the performances of all the devices are dramatically enhanced relative to corresponding species based on P3HT/C 60 active layers. Among all the thermal treatments the mesophase annealing achieves the best performance with a short-circuit current density ( J sc) of 5.5 mA/cm 2, an open-circuit voltage ( Voc) of 0.52 V, a calculated fill factor (FF) of 0.23, and a power conversion efficiency (PCE) of 0.65%, which is 3 times higher than that of the untreated one.

Altered membrane lipid dynamics and chemoprevention by non-steroidal anti inflammatory drugs during colon carcinogenesis.

The present work focuses on the anti-neoplastic role of non steroidal anti-inflammatory drugs (NSAIDs) in modulating the biophysical parameters of the colonic membranes in 1,2-dimethylhydrazine dihydrochloride (DMH) induced carcinogenesis. The steady-state fluorescence polarization technique was applied to assess membrane fluidity, membrane polarity and lipid phase states. The decline in cholesterol content, biosynthesis and cholesterol: phospholipids ratio with DMH treatment indicates more fluidity associated with carcinogenesis. The DMH group had shown lower order parameter indicating more fluidity whereas NSAIDs resulted in increasing the membrane lipid order. The converging effects of these changes were more in membrane phase separations and membrane phase state. In DMH treatment membrane shows lesser phase separation or high polarity, and more liquid crystalline state while for NSAID groups membranes have higher phase separations or low polarity, and more of the gel phase. Further, NSAIDs induced anti-proliferative effects were evidently observed by apoptosis in the colonocytes by using acridine orange-ethidium bromide fluorescent staining and Terminal de-oxynucleotidyl transferase dUTP nick end labeling (TUNEL) assay. The results suggest that NSAIDs induced alteration in the membrane biophysical parameters may be an important initiating event for the chemopreventive action.

Theoretical and experimental study of the interactions of annonaceous acetogenins with artificial lipid bilayers

We report here experimental (FTIR) results and molecular dynamics simulations of the interactions of acetogenins with artificial lipid bilayers. FTIR results indicated that acetogenins interact to different extents with the phosphate and carbonyl groups of membranes in the liquid crystalline state. In this work, molecular dynamics simulations of annonacin ( 1) and rolliniastatin-1 ( 2) in a fully hydrated POPC bilayer were performed in order to investigate the effects caused by these compounds on the hydration patterns surrounding the headgroups of the lipid membrane. Our results enhanced the understanding of the action mechanism of acetogenins in the membrane environment.

Stability of liquid crystalline phases in the phase-field-crystal model

The phase-field-crystal model for liquid crystals is solved numerically in two spatial dimensions. This model is formulated with three position-dependent order parameters, namely the reduced translational density, the local nematic order parameter, and the mean local direction of the orientations. The equilibrium free-energy functional involves local powers of the order parameters up to fourth order, gradients of the order parameters up to fourth order, and different couplings between the order parameters. The stable phases of the equilibrium free-energy functional are calculated for various coupling parameters. Among the stable liquid crystalline states are the isotropic, nematic, columnar, smectic-A, and plastic crystalline phases. The plastic crystals can have triangular, square, and honeycomb lattices and exhibit orientational patterns with a complex topology involving a sublattice with topological defects. Phase diagrams were obtained by numerical minimization of the free-energy functional. Their main features are qualitatively in line with much simpler one-mode approximations for the order parameters.

Effect of temperature on the photobehavior of Rose Bengal associated with dipalmitoylphosphatidyl choline liposomes

The association and photobehavior of Rose Bengal (RB) in the presence of dipalmitoylphosphatidyl choline (DPPC) small unilamellar liposomes is determined by the temperature. At temperatures above the main phase transition of the bilayer, the incorporation of the dye is ca. 2.5 times more efficient than that taking place when the bilayer is in the gel state. In both temperature ranges, adsorption isotherms show a noticeable anti-cooperativity that can be related to electrostatic repulsion between bound molecules. The photophysics and the photochemistry of the bound dye molecules also depend on the bilayer status. In particular, in the liquid crystalline state the surrounding of the dye is more polar and production of singlet oxygen is less efficient ( Φ∼0.1). This reduced singlet oxygen production is partially due to a low triplet yield ( Φ T =0.35) and triplet self-quenching due to a high local RB concentration. In spite of these, tryptophan is efficiently photobleached when RB is associated to liposomes in the liquid crystalline state, probably due to a Type I mechanism favored by its high local concentration in the sensitized surroundings.